1. Field of the Invention
The present invention relates to dye-donor elements for use in thermal dye sublimation transfer methods, the dye-donor elements comprising a subbing layer that improves the adhesion between the polymeric support and the dye/binder layer.
2. Description of the Prior Art
Thermal transfer methods have been developed to make prints from electronic pattern information signals e.g. from pictures that have been generated electronically by means of a colour video camera. To make such prints the electronic picture can be subjected to colour separation with the aid of colour filters. The different colour selections thus obtained can then be converted into electric signals, which can be processed to form cyan, magenta, and yellow electrical signals. The resulting electrical colour signals can then be transmitted to a thermal printer. To make the print a dye-donor element having repeated separate areas of cyan, magenta, and yellow dye is placed in face-to-face contact with a receiving sheet and the resulting sandwich is inserted between a thermal printing head and a platen roller. The thermal printing head, which is provided with a plurality of juxtaposed heat-generating resistors, can selectively supply heat to the back of the dye-donor element. For that purpose it is heated up sequentially in correspondence with the cyan, magenta, and yellow electrical signals, so that dye from the selectively heated regions of the dye-donor element is transferred to the receiver sheet and forms a pattern thereon, the shape and density of which are in accordance with the pattern and intensity of the heat supplied to the dye-donor element.
The dye-donor element usually comprises a very thin support e.g. a polyester support coated on one side with a slipping layer that provides a lubricated surface against which the thermal printing head can pass without suffering abrasion and on the opposite side with a dye/binder layer, which contains the printing dyes in a form that can be released in varying amounts depending on, as mentioned above, how much heat is applied to the dye-donor element.
A very thin polymeric support is necessary to allow the heat generated selectively by the thermal printing head to pass effectively through the support to the dye/binder layer and cause dye to transfer from the selectively heated regions of that layer to the receiver sheet. However, as a result of the extreme thinness of the support the dye/binder layer tends to delaminate under the influence of the heat supplied by the printing head.
To prevent delamination a subbing layer can be provided between the support and the dye/binder layer. Various subbing layers have been described for photographic applications where the adhesion between a polymeric support and a hydrophilic colloid layer, generally gelatin layers had to be improved. Unfortunately, many of them are inappropriate for use in thermal dye sublimation transfer methods. An attempt was made to provide a subbing layer for use in thermal dye sublimation transfer methods. In EP-A 268,179 a subbing layer has been proposed, which comprises a polymer having an inorganic backbone e.g. an organic titanate or titanium alkoxide. However, it was found that the addition of organic titanates did not adequately solve the adhesion problems.